[rollei_list] Re: Old film
- From: Ardeshir Mehta <ardeshir@xxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Sat, 28 May 2005 22:46:15 -0400
Ah. Good to know. Thanks, Richard.
+++++
On 28-May-05, at 8:10 PM, Richard Knoppow wrote:
>> [...] The image, once developed, is pure silver. Silver doesn't
>> deteriorate over time AFAIK. (Does it?)
>>
>> Cheers.
>
> Unfortunately, it can. The silver image can tarnish just
> as silverware does. The tarnish is either silver oxide or
> silver sulfide. If film or paper is not properly fixed and
> washed there are other things that can happen beause of the
> decomposition of the residual chemicals. Degradation of even
> well processed images is common due to atmospheric polutants
> or polutants emitted by storage containers. Peroxides and
> sulfur compounds, both produced in quantity by burning
> fossil fuels are a primary source but even something as
> obscure as the fumes from a fresh paint job in a room can
> attack the iamge.
> Very considerable protection is obtained by toning with a
> sulfiding toner. Other toners that are effective are
> Selenium, if there is enough toning, and Gold toners. Gold
> and Sulfiding toners are commonly used to protect microfilm.
> Photographic materials vary considerably in their
> vulnerability to polutants. The least affected are coarse
> grain negative materials, the most vulnerable are very fine
> grain materials like microfilm and some scientific films,
> and warm tone printing paper.
> There is a very extensive literature on image permancence
> and how to obtain it.
> Chromogenic film has another set of vices because the
> image is composed of dye. A great many dyes are not stable.
> Much of the research in color photography over the last
> fifty years has been in the area of making the images more
> stable. The choice of dyes is limited if they are to be
> compatible with the chromogenic color system. A wider choice
> is available if the dye is indenpendant of the emulsion. It
> is for this reason that Technicolor prints are so stable.
> Many Technicolor prints from the late 1930's still look
> about as they did when new but are probably not projectable
> due to degradation of the nitrate support. The same is true
> for old prints made by the Kodak Dye Transfer process, which
> could use more stable dyes, and for color carbon prints
> which used pigments rather than dyes.
> Silver is more stable than dye but is actually not very
> stable unless toned. Silver sulfide is extremely stable.
> Silver sulfide images are the result of using any of several
> Sulfiding toners, often called Sepia toners. Kodak Brown
> Toner and the very similar Agfa Viradon are examples of such
> toners.
---
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